Definition

and

$(\textit{ candidate key: X'\textit} (X' \subset X ) ) \rightarrow (\textit{ non-key attribute: Y })$

ex

Given

$\textit{ X is non-key attribute }( X \in \bigl{ X1, X2, X3 \bigr} )$

and

$\textit{ Y is candidate key }$

...

only

$\bigl{ X1, X2, X3 \bigr} \rightarrow Y$

is true

and

any such like

$\bigl{ X1 \bigr} \rightarrow Y, \bigl{ X1, X2 \bigr} \rightarrow Y, \bigl{ X2, X3 \bigr} \rightarrow Y ...$

are false ... {1}

then

Functional dependecy is satisfied.

...

when {1} is true

example

$\bigl{ X1 \bigr} \rightarrow Y$ is true

then partial functional dependency is satisfied.

参考元